In the prosthetics field, osseointegration refers to orthopedic solutions to an amputation that involve a device that is integrated with the residual bone and extends linearly beyond the bone and through the skin for external engagement with a prosthetic device. Osseointegration is a well-established therapeutic approach in the context of dental implants. The jaw and oral environment are naturally suited to teeth emerging from bone, through the oral epithelium, and into the oral environment. Further, while teeth are exposed to considerable force, forces acting on teeth are generally vertical, and the teeth are well seated in bone and provide each other lateral support. In contrast, osseointegrated devices implanted in a long bone, such as a femur, pose a challenge, in that the percutaneous site through which the osseointegrated abutment emerges from within the limb to the external environment is not a naturally suited site for a percutaneous device. Additionally, although the forces to which the abutment is typically exposed come primarily from a direction linearly aligned with the abutment, an impacting force may come from any direction and may be very strong and unpredictable.
Osseointegration has become a potentially advantageous therapeutic option for transfemoral or knee disarticulation amputations, especially when a patient has not done well with conventional prosthetic sockets. Prosthetic sockets can be unsatisfactory or fail for patients for a number of reasons, but primarily because of comfort issues. Discomfort is not a trivial complaint for amputees with prosthetics. Sites of discomfort can cause serious skin ulceration and debilitating muscle or bone pain associated with the transfer of force through the residual limb. The theory underlying osseointegration is that by engaging the bone of the residual limb directly, and in an appropriate orientation, the need for a socket is eliminated (thus, eliminating socket-based problems) and the abutment provides a direct, biomechanically appropriate connection with a distal prosthetic element. From the patient perspective, an osseointegrated solution also offers the potential of a less cumbersome and less time consuming daily routine, compared to the use of prosthetic sockets and liners.
Osseointegrated metal abutments for residual limbs, however, have been found to have a number of vulnerabilities. First, the percutaneous site on the residual limb is vulnerable to irritation and infection, even after the site heals following implantation of an osseointegrated abutment. Second, the distally exposed metal abutment is called upon to absorb a considerable level of force (and an associated moment of force) that the host bone needs to absorb. Accordingly, the host bone may be subject to erosion and, in the worst case, fracturing and disintegrating.
Therefore, it would be beneficial to have improved osseointegration devices, which would address at least some of the vulnerabilities described above. The embodiments described below will address at least some of these vulnerabilities.